Fix error when bulk deleting runners

What does this MR do and why?

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This MR fixes an error that happens when a group owner selects multiple runners in a group and tries to delete them. This is because this was only available to admins through the :delete_runners permission. In this MR I'm removing the :delete_runners permission in favor of checking the :delete_runner permission for each runner.

Closes #379191 (closed)

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